Scientists have been investigating nightmares for over a century. Their work has resulted in some seriously bizarre findings, but nothing is more strange than the discovery of what people's most common nightmares are.

A Strange Fact About Nightmares

Before we begin, it's important to be clear about what we mean when we talk about "nightmares." A true nightmare, as defined by sleep researchers and standard diagnostic texts, is a disturbing, emotionally intense dream that ends with the dreamer waking from sleep. It doesn't matter if your psyche just cooked up the most metaphysically sublime dreamscape this side of a bad acid trip – if you don't wake up, the experience is technically classified not as a nightmare, but as a "bad dream." (Also not to be confused with nightmares: night terrors.)

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It's estimated that just 5% of adults suffer from nightmares regularly; and yet, the majority of people (surveys of young adults put the number somewhere between 70- and 90-percent) have still experienced a nightmare at least once in their lives, which actually makes them a fairly widespread phenomenon.

Strangely, we know very little about what people actually dream about when they have nightmares. Part of the problem is that nighmares are so personal. To describe them, we spout anecdotes, relay hearsay in the form of second-hand accounts, or – increasingly – cite pithy internet listicles of dubious merit. And this is one of the biggest challenges for scientists who study dream content, or what we dream about.

Our Murky View of Nightmares

In a study to be published in an upcoming issue of the journal Sleep, clinical psychologist Antonio Zadra – a leader in the field of dream research at the University of Montreal – lists several reasons why a more comprehensive view of nightmare content has yet to take shape. Following a review of twelve studies that have examined nightmare content in adults since 1935 (including three co-authored by himself), Zadra concludes that such investigations tend to "vary greatly in the population examined... and in the instruments used to investigate nightmare content." In the majority of the studies Zadra reviewed, the analysis of nightmare content was based on questionnaires and interviews. But the "gold standard" for the study of nightmares, he writes, is a log or journal, updated daily by a test subject. "Questionnaires or similar retrospective instruments can yield inaccurate dream reports due to the fragile nature of dreams' long term recall," he notes, "as well as memory and saliency biases." Zadra later elaborates:

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When asked to think of a nightmare, most subjects are likely to recall particularly intense, unusual, or otherwise salient nightmares rather than more typical experiences. This may explain why themes of falling and of being chased are among the most frequently reported themes in studies based on questionnaire or interview data while appearing much less frequently in prospective logs.

In more than half of the studies, Zadra notes, the definition of a nightmare itself is inconsistent with the diagnostic standard, "as the awakening criterion is not specified." Such incongruities are, of course, to be expected; as our understanding of something changes, so do our definitions*. By this logic, we would expect earlier publications to work by one definition of nightmare, and, as the field progresses, more and more recent studies to hew closer and closer to the present definition. But this is not what we see. Specification of the awakening criterion is erratic, appearing in some studies but not others – and while the awakening specification makes its first appearance in research published in 1970, it is left out in studies as recent as 2004.

It is with all of the above in mind that we present, ample helpings of salt in hand, some of the common themes that studies of nightmare content have dug up.

Common Nightmare Themes

One of the earliest studies to investigate common nightmare themes was conducted by psychologist Hulsey Cason in the 1930s. Cason performed retrospective interviews with a range of test subjects, including adults, "insane" adults, children, blind students and "feeble-minded" patients. Among the 258 people surveyed, the most commonly reported nightmare themes involved:

1. Animals (27%)

2. Being chased (27%)

3. Death/Murder (26%)

4. Home/Family (22%)

5. Falling (21%)

6. Miscellaneous (19%)

7. Accidents (17%)

Limitations of the study include its dependence on retrospective interviews and its failure to specify the awakening criterion, definining a nightmare instead as a distressing or terrifying dream. If these themes seem vague to you, it's because they are. As you'll soon recognize, this is almost always the case with investigations into nightmare content. But then, dreams, themselves, are notoriously vague, are they not?

Another study, conducted by University of North Carolina-Greensboro psychologists Scott Lawrence and Anthony Celluci in 1978, not only required its test subjects (29 nightmare-suffering students) to maintain a dream log, it's also the first in Zadra's review to make specific mention of the awakening criterion. The researchers conclude that the following are the most common themes in the nightmares of their test subjects:

1. Threat of Physical Harm (16%)

2. Injury/Death of Others (15%)

3. Interpersonal Conflicts (15%)

"The psychological activity that occurs in the waking and sleeping states seems to be a reflection of the general life pattern of the individual, his personal experiences in the past, his present interests and occupations, and his hopes and ambitions for the future."

One of the largest, most comprehensive studies on nightmare themes was published in 2010 by psychologist Michael Schredl of the Central Institute of Mental Health in Manheim, Germany. Schredl examined the thematic content of nightmares in more than 1,000 German adults (defined as over the age of 16) who reported experiencing multiple nightmares per year. The five most common nightmare topics were:

The goal of Zadra's own study was "to obtain a comprehensive and comparative description of prospectively collected bad dream and nightmare narratives" using a large sample size comprising undergraduate students as well as members of the population. He also employed the "gold standard" method of dream collection, which requires test subjects to record their dreams in a log over extended periods of time.

1. Physical aggression (48.6%)

2. Interpersonal Conflicts (21%)

3. Failure or Helplessness (16.2%)

4. Health-Related Concerns and Death (9.1%)

5. Apprehension/Worry (8.7%)

The Most Common Nightmare

What these studies make abundantly clear is that settling on a list of the most common nightmares – let alone the most common nightmare – is no mean task. The studies listed above don't even manage to settle on a leading, universal theme. Of course, it's not difficult to imagine how the events of any given nightmare could be encapsulated by multiple thematic categories. Notice also how certain nightmare themes pop up in several different studies, albeit at different ranks and at higher or lower percentages. Be that as it may, it seems evident that the lack of a universally "Most Common" theme points to either the nebulous nature of nightmares or the difficult nature of their study; more probably, it points to both.

We contacted Zadra for comment, but he was unable speak with us either by phone or by email. When we contacted Schredl to ask about why dream and sleep research has not managed to produce a more coherent picture of nightmare content, he emphasized that findings in such studies depend critically on methodology and sampling standards that are still very much evolving. "It depends whether you use a questionnaire or a dream content analysis, a student sample, a[ group of] nightmare sufferers, or a representative sample, as he did in his 2010 study. "All of these results are valid," he says. The key is finding a way to integrate them.

*Consider, for example, that nightmares have been thought of as "frightening" dreams for close to half a century. More recently, researchers have come to acknowledge that a huge range of emotions are implicated in nightmares, including fear, anger, guilt, disgust, sadness and frustration. Zadra's study suggests that 35% of nightmares and 55% of bad dreams contain primary emotions other than fear. And yet, Zadra notes, few studies have actually investigated this range of emotions in any meaningful way.